In order to maintain species of fish that require continuous movement through the water, an artificial current must be provided in portable tanks or livewells to ensure their survival. Fast swimming fish will school in the current along the perimeter of the tank. The size of the fish that can be maintained is limited by the diameter of the tank. Larger fish would need an extremely large tank to ensure that they can swim without their bodies being continuously curved and causing them damage. These types of tanks are not only stressful for the fish, but cumbersome, and take up valuable deck space for passengers, increase the weight of the boat, and may also cause safety hazards.
Japanese Patent Application JP 59-167396 A (see FIG. 1) discloses a live-fish tank 2 in a fishing boat in which a water jet pipe 3 is provided in a position slightly higher than the bottom face of the live-fish tank, the tank having a hatch 4 at the center of its ceiling. A number of jet holes, which jet out water deflected from the center of the tank 2, are provided on the jet pipe. By jetting out sea water, a whirling stream A is generated in the upper part of the tank 2 for live fish to swim in. The fish tank disclosed by JP 59-167396 A must be large in order to maintain live fish, which is disadvantageous particularly onboard a boat where space and weight are limited.